So it's an unclear sentence and not-so-good use of slashes, as I expected :( Thank you for your kind explanation!

@ColleenV I completely agree with you. Sentences are also written left to right in my mother tongue, Japanese :)

@ColleenV I didn't know that "a shift in English would almost always go from left to right." As you explained, "Shift" meant a right shift in the game. Thank you!

@ColleenV Ah, it makes sense. Actually, I wondered whether the "Shift" in the problem statement meant right shift or left shift. So it's likely that the creator of the game intentionally wrote the problem statement ambiguously. Thank you for your comment!